I don't find it very intuitive, and I haven't found a clear guide online as yet.
I end up "playing" with Word Spacing until I get to an approximation of what I need.
I only ever modify Word Spacing and Letter Spacing.
For Letter Spacing I always use -5% minimum and +5% maximum, For Word Spacing it is a crapshoot between 10% minimum and 200% maximum and many varying numbers in between.
It's a pain, it takes ages, and I'm sure I can't be doing this correctly.. Does anyone have any pointers how this is best acheived? Many thanks if so.